Gravitational Definition and 1000 Threads

Is the redshift of a photon between two events independent of the path? I assume for this question that the the cosmological constant is zero. Chatgpt writes: "In a gravitational field, the redshift can depend on the path taken by the photon. For example, in a Schwarzschild metric (which...

Would astrophysicists be able to locate the end of a worm hole using gravitational microlensing? I strongly suspect the answer is yes, but any "how" methodologies you could toss in would be helpful.

I have now several times come across the situation where the equivalence principle is used to explain why a gravitational field bends light. Here is a very clear presentation of the situation from Hartle: Every time I read about this, I wonder why does nobody ever mention what happens when the...

Could the numerical value of the Gravitational Constant G have a quantum basis? G=(2pi x h-bar) + h/137

Hello, I am trying to get my head around this, maybe someone here can help. I have a force arrow diagram for gravitational forces of both Sun and the Earth. Can someone help me name these forces please. Am I correct in thinking that force 1 is the gravitational force that the Earth exerts on...

My question is why the direction of gravitational field doesn't change relative to moving observer take for example gravitational field in the y direction relative to stationary observer but relative to an observer moving with velocity v in the x direction the field should have x component

What no one has seen before: gravitational waveforms from warp drive collapse Despite originating in science fiction, warp drives have a concrete description in general relativity, with Alcubierre first proposing a spacetime metric that supported faster-than-light travel. Whilst there are...

Has anyone ever discovered 2 or more gravitational lenses perfectly aligned with earth? So one lens magnifies the galaxies behind it and another lens between the first and earth magnifies it even more? Would you even be able to tell if they were?

Hi All, We often read that the gravitational field acts by slowing down clocks. Is there any statement that, with the same simplicity, reports on the action of the gravitational field on lengths measured by observers which are close or far from Earth, for example? Best wishes, DaTario

In GR, if two massive objects distort spacetime, are the effects still "equal and opposite" in some sense? In what sense? It seems that for "equal" to hold, the equations of GR must force the effect of one mass, A, on spacetime at the location of another mass, B, to equal the converse (the...

The reason why I have registered in this forum is because I want to ask questions about a gravitational system... well that is... soon I will post some questions, thank you

So, the formula for Gravitational force is F= Gm1m2/r^2 So a given mass such as the earth and a mass such as much self both contribute to an equal and opposite gravitational force on each other. But we can also think of it separately in terms of just the gravitional field generated. The Earth...

R μν − 1/2g μν R= 8πG/c^4T μν In this formula, if the value of the energy momentum tensor(Tμν) becomes zero, can it become gravitational-free?

Many more questions....please enlighten me on this topic. thank you!

It's a question I've pondered over for years and I've even asked a few people but I've never had a convincing answer. As per the summary, if gravitational lensing is spraying light all over the place like an automatic lawn irrigator, is there any chance some light will do a tour of the universe...

If one were to demonstrate gravity independent of earth's constant gravity, how could it be done? Assuming this would need to be done in space, what minimum proportions of mass would be required to demonstrate gravitational pull to a human's naked eye?

There is a gravitational wave spacetime described by$$g = a(u) (x^2-y^2)du^2 + 2du dw + dx^2 + dy^2$$There is one obvious Killing vector field, ##\partial/\partial w \equiv \partial_w##. To find some more, it's suggested to try:$$X = xf(u) \frac{\partial}{\partial w} + p(u)...

If the gravitational constant had a different value, say a lower value than the present value, and since the gravitational constant is a part of Planck dimensions, such as Planck mass, Planck length, etc., how would quantum and classical processes be affected? Are there problems which use the...

SPOILERS This obviously wouldn't happen to that extent, not without tearing the planet to pieces as well. But might they feel a reduction in weight at all? Obviously it's a pretty hypothetical question without any specifics about the distances to the suns but in theory at least.

If one stands on a large planetary body, like the moon, and throws a large object, like a rock straight up, the object will leave with some velocity, slow down to a stop, and then come back down with the same velocity once it returns to its origin. In Newtonian mechanics, the understanding is...

Why is gravitational red blue shift ruled out as a cause of what we see in stars and galaxy's and such?

I think this is the appropriate subforum. I'm curious as to what approaches have been taken. I know this prediction isn't correct. I can think of at least a couple ways that I could go about this. They may or may not give the same prediction. One approach would be to simply use kinematics, and...

"The Price of Abandoning Dark Matter Is Nonlocality" (Deffayet, Woodard) written in response to "What is the price of abandoning dark matter? Cosmological constraints on alternative gravity theories" (Pardo, Spergel) In a nutshell, as explained after equation 34, by adding a nonlocal...

Hi PF, long time no see. Hope you are all well. Recently I have come into a mental conundrum of a cosmological physical nature. After doing some napkin calculations about the energy of celestial bodies and transforming them into mass via E=mc^2 I've found that said energy is by no means small...

If a mass is moving it has a wavelength - my question is, is the gravitational field of the mass then modulated accordingly ?

Hello everyone, thank you for taking your time to read this. I was assigned a homework task of multiple choice questions to do with gravitational fields. This is one of the last questions and I have been pondering over it for some time now. I don't understand how any sort of answer is...

why is that the gravitational force proportional to product of masses why not sum of masses or something else .........

https://www.sciencealert.com/uncanny-coincidence-fast-radio-burst-detected-after-gravitational-wave-event

Deur Gravitational self-interaction Doesn't Explain Galaxy Rotation Curves this paper A. N. Lasenby, M. P. Hobson, W. E. V. Barker, "Gravitomagnetism and galaxy rotation curves: a cautionary tale" arXiv:2303.06115 (March 10, 2023). Directly comments on Deur's theory of self-interaction...

Let's say we have some observer in some curved spacetime, and we have another observer moving relative to them with some velocity ##v## that is a significant fraction of ##c##. How would coordinates in this curved spacetime change between the two reference frames? For example, imagine a...

Hi, I'm putting together some resources about theories and would like some help to make sure I don't make a mistake. In particular, I'd like to know if each of the electromagnetic, gravitational, mechanical and entropic processes applies to every physical process. So, for example, due to an...

This is of a more philosophical inquiry. If two particles are in a void and moving apart, if they are sufficiently far apart, like say the distance between two galaxy cluster walls, does the gravitational field between them still fundamentally exist? I'm trying to understand if gravity will...

Picture below. Both bodies are made of same material but the body placed in water had 2.4 times greater mass. What is the relationship between buoyancy Force and gravitational force between body in water and body in air?I have no clue how to solve this. I know that body with greater mass has 2.4...

Am I correct in thinking that the gravitational field of the moon passes straight through the Earth as if in a vacuum, to produce a tidal bulge on the opposite side to where the moon is, while the Earth’s much stronger field cannot actually bend or modify it as it passes through but can only add...

Assume you have a two particle system, A, which has a mass and gravitational pull of g, and B, an object with low mass, The system starts at time 0 with the distance between A and B being 0, A being at rest and B having enough kinetic energy to move it a distance r away from A, until time t all...

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Example: The radius of the Earth is 6371 km. It has an average density of 5.5 g/cm3. Earth's inner core has the highest density at 12.9 g/cm3 [more than double the average]. Its surface gravity is measured in units of acceleration, which, in the SI system, are meters per second squared. It may...

I was reading this, but am confused: https://nautil.us/the-remarkable-emptiness-of-existence-256323/

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In Dirac's "General Theory of Relativity", he begins Chap 16, with "Let us consider a static gravitational field and refer it to a static coordinate system. The ##g_{\mu\nu}## are then constant in time, ##g_{\mu\nu,0}=0##. Further, we must have ##g_{m0} = 0, (m=1,2,3)##." It's obvious that...

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I was reading this paper (*Green's functions for gravitational waves in FRW spacetimes:* [https://arxiv.org/abs/gr-qc/9309025](https://arxiv.org/abs/gr-qc/9309025)) and I had a specific question about one statement in the paper that I would like to ask: At page 6, the author says that...

When one mass is held fixed, the other mass acquires a speed v from gravity. I don't understand the following explanation: When both masses can move, they share the kinetic energy, so both have speed v/√2, so the relative speed is √2v. Hence to collapse the same distance r, the latter case will...

For some time I was wondering, what would happen if the Sun just disappeared like someone hit the delete button in Universal Sandbox. Specifically, what kind of gravitational waves will be produced in the wake of such an event? Would the law of conservation of Mass-Energy be miraculously...

I've been thinking about how rotational speeds don't fall off high distances from galactic centers, for which dark matter is generally an explanation for the increase in acceleration Speed = distance / time But time is relative What "time" is used in these calculations? Wouldn't time be...

I'm wondering is whether it is the gravitational potential (in J/kg) at a point in space that determines the rate of passage of time, or whether it is the gravitational field strength (in m/s2). To clarify, suppose you had a very heavy hollow spherical shell. The gravitational potential would...

I solved that the hollowed out mass is M/8, which is correct. I don't understand why it is incorrect to substitute the remaining mass (7M/8) back into the F = G*m1m2/r to produce the force. Why is the solution the force of the whole lead sphere minus the force of the “hole” lead sphere, which is...

I was wondering if we could have an object made up of only electrons. Normally, that wouldn't be possible because electrons repel each other. However, this repulsion can be overcome using gravity. So my question is, how many electrons would you need to have their gravitational attraction...

Imagine a tangran puzzle, in which an extra piece "y", identical to piece 'x', is maliciously added. No matter how hard the player tries, he will never be able to restore the game's original form, that is: a perfect square. This illustration has a clear purpose: If gravitational mass and...

When we derive the formula of the redshift by the equivalence principle we imagine a light ray which goes from the bottom to the top of the elevator and which would take a duration t = h/c to make the journey, with h = height of the elevator. I don't understand why t = h/c, because while the ray...